Single-Photon Emission Computed Tomography/Computed Tomography Imaging in a Rabbit Model of Emphysema Reveals Ongoing Apoptosis In Vivo

Abstract

Evaluation of lung disease is limited by the inability to visualize ongoing pathological processes. Molecular imaging that targets cellular processes related to disease pathogenesis has the potential to assess disease activity over time to allow intervention before lung destruction. Because apoptosis is a critical component of lung damage in emphysema, a functional imaging approach was taken to determine if targeting apoptosis in a smoke exposure model would allow the quantification of early lung damage in vivo. Rabbits were exposed to cigarette smoke for 4 or 16 weeks and underwent single-photon emission computed tomography/computed tomography scanning using technetium99m-rhAnnexin V-128. Imaging results were correlated with ex vivo tissue analysis to validate the presence of lung destruction and apoptosis. Lung computed tomography scans of long-term smoke-exposed rabbits exhibit anatomical similarities to human emphysema, with increased lung volumes compared with controls. Morphometry on lung tissue confirmed increased mean linear intercept and destructive index at 16 weeks of smoke exposure and compliance measurements documented physiological changes of emphysema. Tissue and lavage analysis displayed the hallmarks of smoke exposure, including increased tissue cellularity and protease activity. Technetium99m-rhAnnexin V-128 single-photon emission computed tomography signal was increased after smoke exposure at 4 and 16 weeks, with confirmation of increased apoptosis through terminal deoxynucleotidyl transferase dUTP nick end labeling staining and increased tissue neutral sphingomyelinase activity in the tissue. These studies not only describe a novel emphysema model for use with future therapeutic applications, but, most importantly, also characterize a promising imaging modality that identifies ongoing destructive cellular processes within the lung.

Single-photon emission computed tomography/computed tomography imaging of RAGE in smoking-induced lung injury

“…Mature female New Zealand White Rabbits (approximately 6 months of age with a weight 1.3–1.8 kg) were obtained from Harlan Laboratories (Indianapolis, IN, USA) and Charles River Laboratories (Wilmington, MA, USA). These imaging studies were performed in parallel with the extensive characterization of the rabbit smoke exposure model presented within our Annexin V targeted SPECT/CT imaging studies [17].…”

“…Total particulate matter was maintained at 100–150 mg/m 3 as measured by gravimetric analysis. Rabbits underwent smoke exposure 4 h per day, 5 days per week for 4 or 16-weeks including the day prior to imaging and/or sacrifice (4-weeks n = 5, 16-weeks n = 4) [17]. Age and weight matched rabbits breathing room air were followed over the same time intervals as controls (4-weeks n = 4, 16-weeks n = 4).…”

“…We recently described the development and detailed characterization of a rabbit model of cigarette smoke induced COPD with many of the histopathological and lung functional characteristics of human disease including a neutrophilic airway infiltrate, increased pulmonary compliance, and airspace enlargement [17]. In this model, we also described the in vivo time course of the upregulation of the apoptosis-associated molecule Annexin V, demonstrating a sustained increase in smoke-exposed rabbits after 4-weeks and 16-weeks of smoke exposure when quantified by SPECT/CT, correlating with cellular apoptosis on ex vivo tissue analysis.…”

Reactive Oxygen Species in Chronic Obstructive Pulmonary Disease

“…This may cause emphysema, which leads to the progressive and relentless loss of lung function due to the destruction of lung parenchyma and chronic inflammation. Furthermore, studies from animal models indicate that 4- to 6-month exposure to cigarette smoke leads to emphysema development in mice, rats, and rabbits [ 21 – 23 ]. Exacerbations of COPD are of major global importance [ 24 ].…”

Animal Models of Chronic Obstructive Pulmonary Disease

“…Very few larger animals have been utilized in the whole-body exposure system, perhaps due to insufficient access to chambers large enough to contain these animals. Several studies have successfully exposed rabbits to whole body CS [101][102][103][104][105]. Mice do not produce MMP1, the major collagenase associated with COPD [106], but rabbits express MMP1 and its induction is CS triggered [103].…”